Communication apparatus

ABSTRACT

A wave detecting section of a receiver has a first wavelet transformer involving a plurality of wavelet filters orthogonal to each other for performing a wavelet transform on received waveform data, a Hilbert transformer for performing a Hilbert transform on the received waveform data, a second wavelet transformer having the same configuration as that of the first wavelet transformer for performing a wavelet transform on outputs from the Hilbert transformer, a code converter for inverting the codes of outputs in odd-numbered places among outputs from the second wavelet transformer, a level converter for correcting fluctuations of outputs from the code converter attributable to a ripple of the Hilbert transformer, and a complex data generator for generating complex data, by defining outputs of the first wavelet transformer as in-phase components of the complex information and outputs from the level converter as orthogonal components of the complex information.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication apparatus employing amulti-carrier transmission method (Digital Wavelet Multi-Carriertransmission method, which is hereinafter referred to as “DWMCtransmission method”), which performs data transmission with digitalmodulation and demodulation processes utilizing real coefficient waveletfilter banks.

2. Description of the Related Art

The transmission method involving digital modulation and demodulationprocesses utilizing real coefficient wavelet filter banks is a type ofmulti-carrier modulation method in which a plurality of digitalmodulated waves are synthesized using real coefficient filter banks togenerate a transmission signal. PAM (pulse amplitude modulation) is usedas a method for modulating each carrier.

Data transmission according to the DWMC transmission method will bedescribed with reference to FIGS. 15 to 18. FIG. 16 is a waveformdiagram showing an example of a wavelet waveform. FIG. 16 is a waveformdiagram showing an example of a waveform transmitted according to theDWMC transmission method. FIG. 17 is a spectrum diagram showing anexample of a transmission spectrum according to the DWMC transmissionmethod. FIG. 18 illustrates a frame to show an example of aconfiguration of a frame transmitted according to the DWMC transmissionmethod.

When data are transmitted according to the DWMC transmission method, asshown in FIG. 15, impulse responses of each subcarrier are transmittedin an overlapping relationship with each other in the subcarrier. Eachtransmission symbol becomes a time waveform that is a combination ofimpulse responses in each subcarrier, as shown in FIG. 16. FIG. 17 showsan example of an amplitude spectrum. According to the DWMC transmissionmethod, transmission symbols as shown in FIG. 16 in a quantity rangingfrom several tens to several hundreds are collected to form one frame tobe transmitted. FIG. 18 shows an example of a configuration of a DWMCtransmission frame. The DWMC transmission frame includes symbols forframe synchronization and symbols for equalization in addition tosymbols for transmitting information data.

FIG. 14 is a block diagram of a communication apparatus according to therelated art comprised of a transmitter 299 and a receiver 199 employingthe DWMC transmission method.

In FIG. 14, reference numeral 110 represents an A/D converter; referencenumeral 120 represents an wavelet transformer; reference numeral 130represents a P/S converter for converting parallel data into serialdata; reference numeral 140 represents a judgment unit for judging areceived signal; reference numeral 210 represents a symbol mapper forconverting bit data into symbol data to perform symbol mapping;reference numeral 220 represents an S/P converter for converting serialdata into parallel data; reference numeral 230 represents an inversewavelet transformer; and reference numeral 240 represents a D/Aconverter.

An operation of the communication apparatus having such a configurationwill now be described.

First, at the transmitter 299, the symbol mapper 210 converts bit datainto symbol data, and symbol mapping (PAM modulation) is performedaccording to each item of the symbol data. The serial-to-parallelconverter (S/P converter) 220 supplies each subcarrier with real numbers“di” (i=1 to M, M being a plural number) which are subjected to aninverse discrete wavelet transform on a time axis by the inverse wavelettransformer 230. Thus, sample values having time axis waveforms aregenerated to generate a series of sample values representing transmittedsymbols. The D/A converter 240 converts the series of sample values intoa base band analog signal waveform that is continuous in time, thewaveform being then transmitted. The number of the sample values on thetime axis generated by the inverse discrete wavelet transform isnormally 2 to the n-th power (n is a positive integer).

At the receiver 199, the received signal is converted by the A/Dconverter 110 into a digital base band signal waveform that is thensampled at the same sample rate as that of the transmitter. The seriesof sample values is subjected to a discrete wavelet transform on afrequency axis by the wavelet transformer 120 and thereafterserial-converted by the parallel-to-serial converter (P/S converter)130. Finally, the judgment unit 140 calculates the amplitude of eachsubcarrier to judge the received signal and obtain received data.

Since amplitude distortions and phase distortions can occur duringcommunication because of impedance fluctuations of the transmission pathand the influence of multi-path, a capability of treating both ofamplitude and phase parameters, i.e., complex information will beconvenient. However, the DWMC transmission method according to therelated art does not allow distortions to be corrected depending on thecondition of transmission paths because it is only capable of treatingamplitude information, which results in a problem in that transmissionefficiency is significantly reduced (see the following document, forexample).

Hitoshi KIYA “Digital Signal Processing Series 14, Multi-Rate SignalProcessing”, Shokodo, Oct. 6, 1995, pp. 186–190.

As thus described, a communication apparatus employing a transmissionmethod utilizing real coefficient filter banks according to the relatedart has a problem in that it can treat only amplitude information astransmission data and in that a receiver cannot perform a process fortreating complex information.

SUMMARY OF THE INVENTION

There are demands that such a communication apparatus should use theDWMC transmission method which allows complex information to be treated.

In order to satisfy the demands, the invention provides a communicationapparatus employing the DWMC transmission method that allows complexinformation to be treated.

To solve the problem, the invention provides a communication apparatusemploying a multi-carrier transmission method which performs datatransmission with digital multi-carrier modulation and demodulationprocesses utilizing a real coefficient wavelet filter bank, whichcomprises a receiver that performs a digital multi-carrier demodulationprocess, wherein the receiver having a wave detecting section, the wavedetecting section has: a first wavelet transformer involving M realcoefficient wavelet filters, which are orthogonal with respect to eachother, for performing a wavelet transform of waveform data of receivedsignal; a Hilbert transformer for performing a Hilbert transform of thewaveform data; a second wavelet transformer for performing a wavelettransform of outputs from the Hilbert transformer; and a complex datagenerator for generating complex data, by defining outputs from thefirst wavelet transformer as in-phase components of complex informationand outputs from the second wavelet transformer as orthogonal componentsof the complex information.

Thus, there is provided a communication apparatus employing the DWMCtransmission method that allows complex information to be treated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a wave detecting section that forms a partof a receiver of a communication apparatus according to a firstembodiment of the invention;

FIG. 2 is a block diagram of a wave detecting section that forms a partof a receiver of a communication apparatus according to a secondembodiment of the invention;

FIG. 3 is a block diagram of a wavelet transformer that forms a part ofthe wave detecting sections in FIGS. 1 and 2;

FIG. 4 is a block diagram showing a configuration of the prototypefilter having a polyphase configuration in FIG. 3;

FIG. 5 is a block diagram of a wavelet transformer in FIG. 1;

FIG. 6 is a block diagram showing a configuration of the prototypefilter having a polyphase configuration in FIG. 5;

FIG. 7 is a block diagram of another wavelet transformer (a secondwavelet transformer) in FIG. 1;

FIG. 8 is a block diagram of a receiver that forms a part of acommunication apparatus according to a fifth embodiment of theinvention;

FIG. 9A is a block diagram of a transmitter that forms a part of acommunication apparatus according to a sixth embodiment of theinvention;

FIG. 9B is a block diagram of a receiver that forms a part of thecommunication apparatus according to the sixth embodiment of theinvention;

FIG. 10 is a graph showing a relationship between subcarriers and sinewave frequencies;

FIG. 11 is a block diagram of a wave detecting section that forms a partof a receiver of a communication apparatus according to a seventhembodiment of the invention;

FIG. 12 is a block diagram of a modulator that forms a part of atransmitter of a communication apparatus according to an eighthembodiment of the invention;

FIG. 13A is a block diagram of a transmitter of a communicationapparatus according to a ninth embodiment of the invention;

FIG. 13B is a block diagram of a receiver of the communication apparatusaccording to the ninth embodiment of the invention;

FIG. 14 is a block diagram of a communication apparatus according to therelated art constituted by a transmitter and a receiver employing theDWMC transmission method;

FIG. 15 is a waveform diagram showing an example of a wavelet waveform;

FIG. 16 is a waveform diagram showing an example of a transmissionwaveform according to the DWMC transmission method;

FIG. 17 is a spectrum diagram showing an example of a transmissionspectrum according to the DWMC transmission method;

FIG. 18 illustrates a frame to show an example of a configuration of aframe transmitted according to the DWMC transmission method;

FIG. 19 is a block diagram of a transmitter that forms a part of thecommunication apparatus according to the fifth embodiment of theinvention;

FIG. 20 is a block diagram of a transmitter that forms a part of acommunication apparatus according to a tenth embodiment of theinvention;

FIG. 21 is a block diagram of a receiver that forms a part of thecommunication apparatus according to the tenth embodiment of theinvention; and

FIG. 22 is a block diagram of a power line communication systemaccording to an eleventh embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described withreference to FIGS. 1 to 21. In the following embodiments, a wavelettransform is performed by a cosine modulation filter bank unlessotherwise specified.

(First Embodiment)

FIG. 1 is a block diagram of a wave detecting section that forms a partof a receiver of a communication apparatus according to the firstembodiment of the invention. A transmitter of the same is identical tothe transmitter 299 in FIG. 14 in configuration.

In FIG. 1, reference numeral “101” represents a wave detecting sectionof a receiving unit; reference numeral “102” represents a wavelettransformer for performing a wavelet transform of waveform data ofreceived signal (hereinafter, “received waveform data”); referencenumeral “103” represents a Hilbert transformer for performing a Hilberttransform of the received waveform data; reference numeral “104”represents a wavelet transformer having the same configuration as thatof the wavelet transformer 102 for performing a wavelet transform ofoutputs from the Hilbert transformer; reference numeral “105” representsa code converter for inverting codes in odd-numbered places amongoutputs “di” (i=0 to M, M being a plural number) from the wavelettransformer 104; reference numeral “106” represents a level converterfor correcting fluctuations of the amplitude of data output by the codeconverter 105 attributable to ripple characteristics of the Hilberttransformer 103; and reference numeral “107” represents a complex datagenerator for generating complex data having a real part (I components)which is outputs from the wavelet transformer 102 and an imaginary part(Q components) which is outputs from the level converter 106.

An operation of the communication apparatus having such a configurationwill now be described on an assumption that it accommodates Msubcarriers to which subcarrier numbers 1 to M are assigned.

First, the wavelet transformer 102 performs a wavelet transform ofwaveform data that have been received to obtain a component that is inphase with each of the M subcarriers. The Hilbert transformer 103performs a Hilbert transform of the received waveform data to generatewaveform data in which each frequency component included in the receivedsignal is shifted by π/2, and the wavelet transformer 104 obtains acomponent orthogonal to each subcarrier. At this time, since outputs inodd-numbered places from the wavelet transformer 104 are output withtheir codes inverted, the code converter 105 corrects them. Further, theamplitude of data in each subcarrier has fluctuated because of ripplecharacteristics of the Hilbert transformer 103, and the level converter106 corrects the same. The complex data generator 107 generates complexdata having in-phase components and orthogonal components that areconstituted by outputs from the wavelet transformer 102 and the levelconverter 106, respectively.

Although the present embodiment has been described with reference to theuse of two wavelet transformers having the same configuration, aconfiguration may be employed in which only one wavelet transformer isused. The level converter and the code converter are not required when ahighly accurate Hilbert transformer or an equalizer for amplitudecorrection is used.

Since the present embodiment makes it possible to process not onlyamplitude but also phase information as described above, even if thesynchronization of subcarriers is mistimed because of a bad condition ofthe transmission path attributable to a group delay and so on, the phaserotation of each subcarrier can be corrected to improve receivingperformance.

(Second Embodiment)

FIG. 2 is a block diagram of a wave detecting section that forms a partof a receiver of a communication apparatus according to a secondembodiment of the invention. A transmitter of the same is identical tothe transmitter 299 in FIG. 14 in configuration.

In FIG. 2, reference numeral “108” represents a wave detecting sectionof a receiving unit; reference numeral “109” represents a wavelettransformer for performing a Hilbert transform, a wavelet transform, anda process of inverting codes in odd-numbered places on waveform datathat have been received at a time; and reference numeral “107 a”represents a complex data generator for generating complex data having areal part data (I components) which is outputs from the wavelettransformer 102 and an imaginary part data (Q components) which isoutputs from the wavelet transformer 109.

The apparatus operates substantially the same as the first embodiment,the only difference being the fact that the Hilbert transform, thewavelet transform, and the code inverting process that are performed oneafter another in the first embodiment are performed at a time in thepresent embodiment.

Such a configuration allows faster processing than the configurationdescribed in the first embodiment and also allows simpler circuitry.

(Third Embodiment)

FIG. 3 is a block diagram of the wavelet transformer 102 that forms apart of the wave detecting sections in FIGS. 1 and 2. FIG. 4 is a blockdiagram showing a configuration of the prototype filter having apolyphase configuration in FIG. 3. FIG. 5 is a block diagram of thewavelet transformer in FIG. 1. FIG. 6 is a block diagram showing aconfiguration of the prototype filter having a polyphase configurationin FIG. 5.

In FIG. 3, reference numeral “102” represents a wavelet transformer asshown in FIG. 1 or 2; reference numeral “121” represents delay elementsfor delaying waveform data received by one sampling period; referencenumeral “122” represents down samplers for reducing the sampling ratefor the received waveform data by a factor of M; reference numeral “123”represents a prototype filter; and reference numeral “124” represents afast discrete cosine transformer (TYPE 4). In FIG. 3, the quantities ofthe delay elements 121 and the down samplers 122 used are M−1 and M,respectively.

In FIG. 4, reference numeral “123” represents the prototype filter shownin FIG. 3; reference numeral “131” represents multipliers having thesame filter coefficient as that of the prototype filter; referencenumeral “132” represents two-input adders; and reference numeral “133”represents delay elements for introducing a delay for one symbol period(M sampling periods). The order of the prototype filter 123 shown inFIG. 4 is 2M.

In FIG. 5, reference numeral “109A” represents a wavelet transformerhaving the same function as that of the wavelet transformer 109 in FIG.2; reference numeral “121” represents delay elements for delayingwaveform data received by one sampling period; reference numeral “122”represents down samplers for reducing the sampling rate of the receivedwaveform data by a factor of M; reference numeral “125” represents aprototype filter; and reference numeral “126” represents a fast discretesine transformer (TYPE 4). The quantities of the delay elements 121 andthe down samplers 122 are M−1 and M, respectively.

In FIG. 6, reference numeral “125” represents the prototype filter shownin FIG. 5; reference numeral “131” represents a multiplier having thesame filter coefficient as that of the prototype filter; referencenumeral “132” represents a two-input adder; and reference numeral “133”represents delay elements for introducing a delay of one symbol period(M sampling periods). The order of the prototype filter shown in FIG. 6is 2M.

The apparatus is the same as the second embodiment in operation anddifferent from the same in that the part constituted by FIR filters inthe second embodiment is replaced by the prototype filter having apolyphase configuration in combination with the use of a discrete cosinetransform or discrete sine transform in the present embodiment.

While the first wavelet transformer (the wavelet transformer 102) andthe second wavelet transformer (the wavelet transformer 109A) of thepresent embodiment are configured as completely separate elements, theymay share the same circuitry obviously, this is possible because theprototype filters of the transformers have filter coefficients that aremerely inverted from each other and because a discrete cosine transformand a discrete sine transform are different only in that the processesuse different coefficients.

The above-described configuration allows faster processing than theconfiguration described in the second embodiment because the polyphaseconfiguration involves a smaller amount of calculation than that in theFIR filter configuration.

(Fourth Embodiment)

FIG. 7 is a block diagram of a wavelet transformer (the second wavelettransformer) in FIG. 1.

In FIG. 7, reference numeral “109A” represents a wavelet transformerhaving the same function as that of the wavelet transformer 109 in FIG.5; reference numeral “121” represents delay elements for delayingwaveform data that have been received by one sampling period; referencenumeral “122” represents down samplers for reducing the sampling rate ofthe received waveform data by a factor of M; reference numeral “125”represents a prototype filter; reference numeral “127” represents a timeseries inverter for inverting the time sequence of every M samples in aseries of inputs; reference numeral “124” represents a fast discretecosine transformer (TYPE 4); and reference numeral “128” represents acode converter for inverting codes in odd-numbered places of the inputdata. In FIG. 5, the quantities of the delay elements 121 and the downsamplers 122 are M−1 and M, respectively.

The apparatus is the same as the third embodiment in operation anddifferent from the same in that the part constituted by the discretesine transformer 128 in the third embodiment is replaced by the timeseries inverter 127, the discrete cosine transformer 124, and the codeconverter 128 in the present embodiment. While the present embodimenthas a configuration in which the time series inverter 127 is providedbefore the discrete cosine transformer 124 and in which the codeconverter 128 is provided after the discrete cosine transformer 124, thetime series inerter 127 and the code converter 128 may be transposedwith the same results.

The above-described configuration allows faster processing than theconfiguration shown in the second embodiment. Since the part constitutedby the discrete cosine transformer 124 and the discrete sine transformer126 in the third embodiment can be constituted only by the discretecosine transformer 124, circuit sharing is allowed to achieve a smallercircuit scale.

(Fifth Embodiment)

FIG. 8 is a block diagram of a receiver that forms a part of acommunication apparatus according to a fifth embodiment of theinvention. A transmitter of the same is identical to that in FIG. 14.

In FIG. 8, reference numeral “100” represents the receiver; referencenumeral “110” represents an A/D converter; reference numeral “108 a”represents a wave detecting section similar in configuration to thatshown in FIG. 1 or 2; reference numeral “120” represents an equalizer;reference numeral “130” represents a parallel-to-serial converter (P/Sconverter); and reference numeral “140” represents a judgment unit.

An operation of the receiver having such a configuration will now bedescribed.

At the receiver 100, the A/D converter 110 performs digital conversionon a signal that has been received to obtain received waveform data. Thewave detecting section 108 a detects the received waveform data andobtains complex information on a plurality of subcarriers included inthe received signal as its output. Next, the equalizer 120 obtainsequalizing quantities by comparing the complex information obtained fromthe wave detecting section 108 a with known data that are allocated inadvance for the purpose of equalization. The complex information isequalized using the equalizing quantities thus obtained in the intervalof actual data transmission symbols and supplied to theparallel-to-serial converter 130. Finally, the judgment unit 140 judgesthe data based on the equalized complex information. This is a series ofoperations performed in the receiver 100. The equalizer 120 obtainsdeviations of the amplitude and phase of each subcarrier from a knownsignal as equalizing quantities. An adaptive filter (LMS or RLS filter)utilizing a plurality of taps may be used depending on transmissionpaths.

The above-described configuration allows accurate demodulation even in atransmission path in a bad condition.

The equalizer 120 of the present embodiment may be used in the mannerdescribed below.

FIG. 19 is a block diagram of the transmitter that forms a part of thecommunication apparatus according to the fifth embodiment of theinvention.

In FIG. 19, reference numeral “200” represents the transmitter;reference numeral “201” represents a synchronization data generator forgenerating the same data for each of subcarriers for the duration ofseveral consecutive symbols; reference numeral “210” represents a symbolmapper for performing symbol mapping (PAM modulation) according to thesynchronization data; reference numeral “230” represents an inversewavelet transformer; reference numeral “220” represents aserial-to-parallel (S/P) converter for performing serial conversion ofoutputs from the inverse wavelet transformer; reference numeral “240”represents a D/A converter for converting waveform data to betransmitted output by the serial-to-parallel converter 220.

An operation of the communication apparatus having such a configurationwill be described with reference to FIG. 10. FIG. 10 is a graph showinga relationship between subcarriers and sine wave frequencies. Forsimplicity of description, it is assumed that eight wavelet transforms,i.e., eight subcarriers are used.

At the transmitter 200, the synchronization data generator 201 firstoutputs the same data (e.g., 1) for each of the subcarriers to thesymbol mapper 210 for the duration of several consecutive symbols. Thedata allocated to each subcarrier at this time are data that are knownto the receiver 100. The data are then transformed by the inversewavelet transformer 230. At this time, the inverse wavelet transformer230 outputs a composite wave originating from sine waves havingfrequencies “fn” as shown in FIG. 10. The composite wave data areconverted by the serial-to-parallel converter 220 and the D/A converter240 into an analog signal that is then transmitted.

At the receiver 100, the A/D converter 100 first performs digitalconversion of the received signal to obtain received waveform data. Thewave detecting section 108 detects the received waveform data andobtains complex information on the plurality of sine waves included inthe received signal as its output. The wave detecting section 108supplies the complex data (complex information) to the equalizer 120.The equalizer 120 synthesizes (2n−1)-th and 2n-th outputs (1≦n≦(M/2−1),the subcarriers being numbered from 0 to M−1) by matching their phasesusing the complex information obtained from the wave detecting section108 to obtain an equalization coefficient to be used for each of thesubcarriers with high accuracy. Equalizing quantities are determinedusing the equalization coefficients thus obtained and known data thatare allocated in advance for the purpose of equalization. This methodcan be carried out because the equalization coefficients are obtainedusing the same sine waves for the (2n−1)-th and 2n-th subcarriers. Thecomplex data are then equalized using equalizing quantities thusobtained in the interval of actual data transmission symbols and aresupplied to the parallel-to-serial converter 130. Finally, the judgmentunit 140 judges the data based on the equalized complex data.

In the above-described configuration, since an equalizing quantity canbe obtained for each pair of subcarriers, calculations can be performedwith accuracy higher than that achieved by determining an equalizingquantity for each subcarrier.

(Sixth Embodiment)

FIG. 9A is a block diagram of a transmitter that forms a part of acommunication apparatus according to a sixth embodiment of theinvention, and FIG. 9B is a block diagram of a receiver that forms apart of the communication apparatus according to the sixth embodiment ofthe invention.

A receiver 100, A/D converter 110, a wave detecting section 108 a, anequalizer 120, a P/S converter 130, and a judgment unit 140 in FIG. 9Bare similar to those in FIG. 8, and they are indicated by line referencenumerals and will not be described here. In FIG. 9B, reference numeral“141” represents a delay circuit for introducing a delay of one samplingperiod; reference numeral “142” is a complex divider; reference numeral“143” represents a complex adder for cumulatively adding complex datainput thereto; reference numeral “144” represents a synchronizationshift calculator; and reference numeral “145” represents asynchronization timing estimation circuit. In FIG. 9A, reference numeral“200” represents the transmitter; reference numeral “201” represents asynchronization data generator for generating the same data for eachsubcarrier for the duration of several consecutive symbols; referencenumeral “210” represents a symbol mapper for performing symbol mapping(PAM modulation) according to the synchronization data; referencenumeral “230” represents an inverse wavelet transformer; referencenumeral “220” represents a serial-to-parallel converter (S/P converter)for performing serial conversion of outputs from the inverse wavelettransformer; and reference numeral “240” represents a D/A converter forconverting waveform data to be transmitted output by theserial-to-parallel converter 220 into an analog signal.

An operation of the communication apparatus having such a configurationwill be described with reference to FIG. 10. FIG. 10 is a graph showinga relationship between subcarriers and sine wave frequencies. Forsimplicity of description, it is assumed that eight wavelet transforms,i.e., eight subcarriers are used.

At the receiver 200, the synchronization data generator 201 firstoutputs the same data (e.g., 1) for each of the subcarriers to thesymbol mapper 210 for the duration of several consecutive symbols. Thedata allocated to each of the subcarriers at this time are data that areknown to the receiver 100. The data are transformed by the inversewavelet transformer 230. At this time, the inverse wavelet transformer230 outputs a composite wave originating from sine waves havingfrequencies “fn” as shown in FIG. 10. The composite wave data areconverted by the serial-to-parallel converter 220 and the D/A converter240 into an analog signal that is then transmitted.

At the receiver 100, the D/A converter 110 first performs digitalconversion of the received signal to obtain received waveform data. Thewave detecting section 108 a detects the received waveform data andobtains complex information on the plurality of sine waves included inthe received signal as its output. At this time, the values of alloutputs from the wave detecting section 108 a are equal when the symbolsare synchronized at accurate timing. When there is mistiming ofsynchronization, the outputs are at values that reflect phase rotationsrepresented by “2πfc·τ” depending on the degrees “τ” of the shifts andthe subcarrier frequencies “fc”. Next, the delay circuit 141 and thecomplex divider 142 perform complex division between adjacentsubcarriers to calculate phase differences on the complex coordinates.Since frequency intervals “fi” between pairs of adjacent subcarriers areall equal, all of the phase differences (complex values) have the samevalue of “2πfi·τ” (in practice, their values deviate from “2πfi·τ” underthe influence of the transmission path). The phase differences “θc”between the subcarriers are cumulatively added by the complex adder 143to obtain an average value “θm”, and the synchronization shiftcalculator 144 obtains synchronization shifts “τm” from the subcarrierintervals “fi” and the average subcarrier phase difference “θm”. Theresults are supplied to the synchronization timing estimation circuit145 to provide feedback of the timing of synchronization to the wavedetecting section 108 a. The average subcarrier phase difference issubtracted from each subcarrier phase difference (θc–θm) to obtain a newparameter “c” (subcarrier phase difference number) with which thesynchronization shift calculator 144 identifies a difference “τc”between the synchronization timing of each subcarrier and averagesynchronization timing to calculate the shift of synchronization timingof each subcarrier from the average synchronization timing. Thesynchronization timing of each subcarrier is subjected to fineadjustment using the difference “τc”. The fine adjustment is requiredbecause the timing of synchronization of each subcarrier is shiftedunder the influence of the transmission path and must be adjusted to theaverage value. However, since the average value does not representperfect synchronization of each subcarrier, any shift of thesynchronization timing of each subcarrier from the averagesynchronization timing is identified, and the synchronization timing ofeach subcarrier is fine-adjusted according to the amount of the shift.The above-described operation makes it possible to correct any shift ofsignal points between the received and known signals (of thesynchronization data) attributable to a shift of the synchronizationtiming of each subcarrier. This allows the performance of subsequentequalization and, consequently, receiving performance to be improved.

After the timing of synchronization is established, the wave detectingsection 108 a supplies the complex data (complex information) to theequalizer 120. The equalizer 120 compares the complex data provided bythe wave detecting section 108 a and the known data that are allocatedin advance for the purpose of equalization (synchronization) to obtainequalizing quantities. The complex data are equalized using theequalizing quantities thus obtained in the interval of actual datatransmission symbols and are supplied to the parallel-to-serialconverter 130. Finally, the judgment unit 140 judges the data based onthe equalized complex data.

With the above-described configuration, since the timing ofsynchronization can be estimated with high accuracy even for atransmission path in a bad condition, demodulation can be performed withhigh accuracy.

Referring to the values determined by the wave detecting section 108 a,quantities of phase rotation can be determined with high accuracy bysynthesizing the (2n−1)-th and 2n-th outputs (1≦n≦(M/2−1), thesubcarriers being numbered from 0 to M−1) while matching their phases.This method can be carried out because the quantities of phase rotationof the (2n−1)-th and 2n-th subcarriers are determined using the samesine wave, as shown in FIG. 10.

With the above-described configuration, since the quantity of a phaserotation attributable to mistiming of synchronization can be determinedfor each pair of subcarriers, calculations can be performed withaccuracy higher than that achievable in determining the quantity of aphase rotation for each subcarrier.

(Seventh Embodiment)

FIG. 11 is a block diagram of a wave detecting section that forms a partof a receiver of a communication apparatus according to a seventhembodiment of the invention. A transmitter of the same is identical tothat shown in FIG. 9B.

In FIG. 11, reference numeral “151” represents the wave detectingsection of the receiver; reference numeral “152” represents a wavelettransformer constituted by M real coefficient wavelet filters that areorthogonal to each other; reference numeral “153” represents complexdata generators for generating complex data, in-phase components (Ichannel) of the complex information being (2n−1)-th outputs from thewavelet transformer 152 and orthogonal components (Q channel) of thesame being 2n-th outputs from the same (1≦n≦(M/2)); and referencenumeral “154” represents a parallel-to-serial converter (P/S converter)for performing serial conversion of the complex data that are seriallyoutput.

An operation of the wave detecting section 151 having such aconfiguration will be described with reference to FIG. 10. Forsimplicity, the description will be made on an assumption that there areeight subcarriers. In the present embodiment, it is assumed that acomposite wave originating from sine waves having frequencies indicatedby the bold solid lines (f1, f2, and f3) in FIG. 10 is input to thereceiver and that the sine waves have phases φ1, φ2, and φ3,respectively. At this time, each sine wave is in an arbitrary phase “φn”(n=1, 2, or 3) in the range from −π to π.

The wave detecting section 151 performs a wavelet transform of waveformdata that have been received with the wavelet transformer 152. At thistime, (2n−1)-th and 2n-th subcarrier outputs (1≦n≦(M/2−1), thesubcarriers being numbered from 0 to M−1) are cos(φn) and sin(φn),respectively, of sine waves having frequencies fn in FIG. 10. Thecomplex data generators 153 generate complex data including real partdata that is constituted by the cos(φn) and imaginary part data that isconstituted by the sin(φn). Finally, the parallel-to-serial converter154 obtains serial complex data.

While the present embodiment employs (M/2−1) complex data generators153, it can be carried out using a single complex data generator byperforming parallel-to-serial conversion of outputs from the wavelettransformer 152 and performing timing control such that (2n−1)-th and2n-th items of the serial data are input to the complex data generator153.

The above-described configuration makes it possible to obtain complexinformation (complex data) with a smaller amount of calculation (aboutone half of that in the third embodiment), although it is limited to areceived signal constituted by sine waves.

(Eighth Embodiment)

FIG. 12 is a block diagram of a modulator that forms a part of atransmitter of a communication apparatus according to an eighthembodiment of the invention.

In FIG. 12, reference numeral “251” represents the modulator; referencenumeral “252” represents a symbol mapper for converting bit data intosymbol data to perform symbol mapping (QAM modulation) according to eachitem of the symbol data; reference numeral “253” represents aserial-to-parallel converter (S/P converter) for performing parallelconversion of items of data input thereto one after another; referencenumeral “254” represents complex data decomposers for decomposingcomplex data input thereto into a real part and an imaginary part; andreference numeral “255” represents an inverse wavelet transformer.

An operation of the modulator 251 of the transmitter having such aconfiguration will be described with reference to FIG. 10. Forsimplicity, the description will be made on an assumption that there areeight subcarriers. In the present embodiment, it is assumed that thetransmitter outputs a composite wave originating from sine waves havingfrequencies indicated by the bold solid lines (f1, f2, and f3) in FIG.10 and that the sine waves have phases φ1, φ2, and φ3, respectively. Atthis time, each sine wave is in an arbitrary phase “φn” (n=1, 2, or 3)in the range from −π to π.

First, the modulator 251 converts data to be transmitted (bit data) intosymbol data with the symbol mapper 252, and QAM modulation is performedaccording to the symbol data to provide signal points on complexcoordinates. The following equation 1 is obtained from this process.e^(jφn)  Equation 1

Next, the data are converted by the serial-to-parallel converter 253into parallel complex data, and each item of the complex data isdecomposed by the complex data decomposer 254 into real part data(cos(φn)) and imaginary part data (sin(φn)). The cos(φn) and sin(φn) arerespectively allocated to (2n−1)-th and 2n-th inputs to the inversewavelet transformer 255 (1≦n≦(M/2−1)). Then, the inverse wavelettransformer 255 outputs a composite wave originating from sine waveshaving frequencies fn as shown in FIG. 10 and initial phases φn andcos(2πfn·t+φn).

While the present embodiment employs M/2−1 complex data decomposers intotal, it can be carried out using only one complex data decomposer.

In the above-described configuration, since an initial phase on acomplex coordinate plane provided by the symbol mapper 252 can be freelyassigned to each of the subcarriers (to be exact, each of pairsconsisting of (2n−1)-th and 2n-th subcarriers), an instantaneous peakvoltage at the transmission of an output can be suppressed by settingthe data such that the phases of the subcarriers do not overlap.

(Ninth Embodiment)

FIG. 13A is a block diagram of a transmitter that forms a part of acommunication apparatus according to a ninth embodiment of theinvention, and FIG. 13B is a block diagram of a receiver of thecommunication apparatus according to the ninth embodiment of theinvention.

In FIG. 13B, reference numeral “150” represents the receiver; referencenumeral “110” represents an A/D converter for converting a signal thathas been received into a digital signal; reference numeral “151”represents a wave detecting section as shown in FIG. 11; referencenumeral “146” represents a phase rotator for rotating a phase on acomplex plane; reference numeral “141” represents a delay circuit forintroducing a delay of one sampling period; reference numeral “142”represents a complex divider; reference numeral “143” represents acomplex adder for cumulatively adding complex data input thereto;reference numeral “144” represents a synchronization shift calculator;and reference numeral “145” represents a synchronization timingestimation circuit. In FIG. 13A, reference numeral “250” represents thetransmitter; reference numeral “256” represents a synchronization datagenerator for generating the same data for each subcarrier for theduration of several consecutive symbols; reference numeral “251”represents a modulator as shown in FIG. 12; and reference numeral “240”represents a D/A converter for converting waveform data to betransmitted generated by the modulator 251 into an analog signal.

Operations of the transmitter 250 and the receiver 150 of thecommunication apparatus having such a configuration will be describedwith reference to FIG. 10. It is assumed that eight wavelet transforms,i.e., eight subcarriers are used.

At the transmitter 250, the synchronization data generator 256 firstoutputs the same data for each subcarrier to the modulator 251 for theduration of several consecutive symbols. The data allocated to eachsubcarrier are data that are known to the receiver 150. Thesynchronization data are modulated by the modulator 251. At this time,the modulator 251 outputs a composite wave originating from sine waveshaving frequencies fn as shown in FIG. 10. The phase of each of the sinewaves depends on the input synchronization data, and the phase isrepresented by φn here. Finally, the composite wave data are convertedby the D/A converter 240 into an analog signal that is then transmitted.

At the receiver 150, the D/A converter 110 first performs digitalconversion of the signal thus received to obtain received waveform data.The wave detecting section 151 detects the received waveform data toobtain complex signal point information on each of the plurality of sinewaves included in the received signal. Since the complex signal pointinformation thus obtained has phases that have been rotated by “φn”, thephase rotator 146 returns the phases by “φn” on the complex coordinates.The values of all outputs from the phase rotator 146 are equal when thesymbols have been synchronized at accurate timing. When thesynchronization has been mistimed, the values reflect phase rotations of“2πfc·τ” that depend on degrees “τ” of shifts and subcarrier frequencies“fc”. Next, the delay elements 141 and the complex divider 142 performcomplex division between adjacent subcarriers to calculate phasedifferences on the complex coordinates. Since all of the pairs ofadjacent subcarriers have the same frequency interval “fi”, allsubcarrier phase differences (complex values) are at the same value of“2πf·τ” (in practice, the values deviate from “2πfi·τ” under theinfluence of the transmission path). The subcarrier phase differencesare cumulatively added by the complex adder 143 to obtain an averagevalue “φm”, and the synchronization shift calculator 144 determines asynchronization shift value “τ” from the subcarrier frequency interval“fi” and the average subcarrier phase difference “φm”. The result issupplied to the synchronization timing estimation circuit 145 to providefeedback of the synchronization timing to the wave detecting section.

With the above-described configuration, the part constituted by twowavelet transformers in the sixth embodiment can be provided using asingle wavelet transformer, which allows a reduction in the scale of thecircuit.

(Tenth Embodiment)

While the invention may be applied to a wide variety of communicationapparatus for transmitting and receiving signals, it is suitable forsystems for power line communication that may employ a transmission pathin a bad condition.

FIG. 20 is a block diagram of a transmitter that forms a part of acommunication apparatus according to a tenth embodiment of theinvention, and FIG. 20 is a block diagram of a receiver that forms apart of the communication apparatus according to the tenth embodiment ofthe invention.

In FIG. 20, reference numeral “600” represents a transmitting section;reference numeral “610” represents a symbol mapper for converting bitdata into symbol data and mapping the same into a certain arrangement ofsignal points; reference numeral “220” represents an S/P converter forconverting serial data into parallel data; reference numeral “620”represents a modulator utilizing a filter bank involving a plurality Mof filters, which are orthogonal with respect to each other formodulating a signal to be transmitted by performing an inverse transformof the same; reference numeral “240” represents a D/A converter forconverting a digital signal into an analog signal; reference numeral“700” represents a receiving section; reference numeral “110” representsan A/D converter for converting an analog signal into a digital signal;and reference numeral “630” represents a demodulator utilizing a filterbank involving a plurality M of filters, which are orthogonal withrespect to each other for demodulating a received signal by transformingthe same.

An operation of this apparatus will now be described with reference toFIGS. 20 and 21.

At the transmitting section 600 of the transmitter, the symbol mapper610 converts bit data into symbol data and maps the same according tocertain signal point mapping information; the filter bank type modulator620 modulates the signal to be transmitted which issignal-points-arranged by the symbol mapper 610 by performing an inversetransform of the same; and the D/A converter 240 converts the digitalsignal into an analog signal. At the wave detecting section 700 of thereceiver, the A/D converter 110 converts the analog signal into adigital signal, and the filter bank type demodulator 630 demodulates thereceived signal by transforming the same. Filter banks that can be usedinclude wavelet-based cosine transform filter banks and FFT-based pulseshaping type OFDMs. The figure illustrates an amplitude spectrumobtained using a cosine modulation filter bank (having a filter lengthof 4M). In the figure, notches are formed by disabling subcarriers thatoverlap amateur radio bands. Multi-carrier transmission usingband-limited (pulse shaped) subcarriers can be performed by carrying outmodulation and demodulation processes using filter banks as thusdescribed. The use of band-limited multi-carriers allows power linecommunication to be more resistant to narrow band interference waves andinter-carrier interference. Since the band of each subcarrier islimited, sharp notches can be formed by disabling several subcarriers.

Deregulation is in progress to allow the use of the band from about 2 Mto 30M for power line communication. However, other existing systems(e.g., amateur radios and shortwave broadcasts) use the same band. Sinceno interfere with such other existing systems is allowed, signals shouldnot be transmitted to the band used by other existing systems duringpower line communication. Normally, a notch filter is generated by aseparate filter to disable transmission to the band used by existingsystems. A notch filter for 30 dB is used in “HomePlug 1.0” released byHomePlug that is an alliance of power line communication businesses inthe United States. Thus, a possible target for the suppression ofinterference to other existing systems is 30 dB or more.

According to the inventive method, a filter bank is used to limit theband of each subcarrier to disable subcarriers that overlap the bandused by existing systems, which makes it possible to achieve the sameoperation as in the method of the related art (the operation ofgenerating notches in the band used by other existing systems; see thefigure) without generating a notch filter. Deeper notches are formed,the greater the filter length of each of the filters of the filter bank(with the number M of the filters fixed). In this case, there is aconcern about a delay attributable to the filters (a filter delay is atrade-off for the notch depth). It is therefore possible to form notchesof 30 dB or more and to suppress a filter delay by limiting the filterlength of a filter bank for power line communication to 4M.

(Eleventh Embodiment)

FIG. 22 is a block diagram of a power line communication systemaccording to an eleventh embodiment of the invention. In the figure,reference numeral “800” represents a building; reference numeral “810”represents a power line; reference numeral “820” represents a telephonenetwork, an optical network, or a CATV network; reference numeral “700”represents communication apparatus utilizing a filter bank involving aplurality M of filters, which are orthogonal with respect to each otheraccording to the invention; reference numeral “710” represents an AVapparatus such as a television set, a video, a DVD, or a DV camera;reference numeral “720” represents a communication apparatus such as arouter, an ADSL, a VDSL, a media converter, or a telephone; referencenumeral “730” represents a documentation apparatus such as a printer, afacsimile, or a scanner; reference numeral “740” represents a securityapparatus such as a camera key or an interphone; reference numeral “750”represents a personal computer; and reference numeral “760” represents ahome electrical apparatus such as an air conditioner, a refrigerator, awashing machine, or a microwave oven.

An operation of the present embodiment will be described with referenceto FIG. 22. The apparatus form a network through the power line andperform bidirectional communication using the communication apparatusutilizing a filter bank involving a plurality M of filters which areorthogonal with respect to each other. Referring to communication to theinternet, a connection may be made via a home gateway provided in thebuilding through the power line. Alternatively, a connection may be madevia a communication apparatus that communicates over the telephonenetwork, optical network, or CATV network as a medium. Furtheralternatively, a connection may be made on a wireless basis from acommunication apparatus having a radio function. Since the communicationapparatus used here perform modulation and demodulation processes usingfilter banks involving a plurality M of filters which are orthogonalwith respect to each other as described in the tenth embodiment,interference with the other existing systems can be suppressed bydisabling subcarriers that overlap the band used by the other existingsystems. Further, since the filter length is limited to 4M, delaysattributable to the filters can be suppressed while achieving a notchdepth of 30 dB or more. On the contrary, the effect of narrow bandinterferences from the other existing systems can be reduced.

Further, when a notch is to be generated in a certain band, what isrequired is only to disable any subcarrier that overlaps the band. It istherefore possible to comply with regulations in various countrieseasily with flexibility. Even when there is a regulation change afterthe present system is put in use, it can be accommodated withflexibility through an action such as firmware upgrading.

1. A communication apparatus employing a multi-carrier transmissionmethod which performs data transmission with digital multi-carriermodulation and demodulation processes utilizing a real coefficientwavelet filter bank, the communication apparatus comprising a receiverthat performs a digital multi-carrier demodulation process, wherein thereceiver having a wave detecting section, the wave detecting sectionhas: a first wavelet transformer involving M real coefficient waveletfilters, which are orthogonal with respect to each other, for performinga wavelet transform of waveform data of received signal; a Hilberttransformer for performing a Hilbert transform of the waveform data; asecond wavelet transformer for performing a wavelet transform of outputsfrom the Hilbert transformer; and a complex data generator forgenerating complex data, by defining outputs from the first wavelettransformer as in-phase components of complex information and outputsfrom the second wavelet transformer as orthogonal components of thecomplex information.
 2. The communication apparatus according to claim1, further comprising: a code converter for inverting codes of outputsin odd-numbered places among M outputs from the second wavelettransformer.
 3. The communication apparatus according to claim 2,further comprising: a level converter for correcting fluctuation ofamplitude of outputs from the code converter, which is caused by aripple of the Hilbert transformer.
 4. The communication apparatusaccording to claim 1, wherein the first wavelet transformer has a firstprototype filter including a first polyphase filter which possesses areal coefficient, M down samplers, M−1 one-sample delaying elements, anda fast M-points discrete cosine transformer (M is an integer not lessthan 2), and the second wavelet transformer has a second prototypefilter including a second polyphase filter which possesses a realcoefficient, M down samplers, M−1 one-sample delaying elements, and afast M-points discrete sine transformer.
 5. The communication apparatusaccording to claim 1, wherein the second wavelet transformer has a thirdprototype filter including a second polyphase filter which possesses areal coefficient, M down samplers, M−1 one-sample delaying elements, atime series inverter for inverting sequence of every M inputs among aninput series, a fast M-points discrete cosine transformer, and a codeconverter for inverting codes in odd-numbered places in the inputseries.
 6. The communication apparatus according to claim 1, wherein thereceiver further has: an equalizer for performing equalization usingboth complex information obtained from the wave detecting section andknown signal for equalization that is previously assigned for theequalization process; and a decision unit for making a decision using asignal obtained from the equalizer.
 7. A communication apparatusemploying a multi-carrier transmission method which performs datatransmission with digital multi-carrier modulation and demodulationprocesses utilizing a real coefficient wavelet filter bank, thecommunication apparatus comprising a receiver that performs a digitalmulti-carrier demodulation process, wherein the receiver having a wavedetecting section, the wave detecting section has: a first wavelettransformer involving M real coefficient wavelet filters, which areorthogonal with respect to each other, for performing a wavelettransform of waveform data of received signal; a second wavelettransformer involving wavelet filters for performing a Hilberttransform, a wavelet transform, and an inversion of codes inodd-numbered places, for the waveform data; and a complex data generatorfor generating complex data, by defining outputs from the first wavelettransformer as in-phase components of the complex information andoutputs from the second wavelet transformer as orthogonal components ofthe complex information.
 8. A communication apparatus employing amulti-carrier transmission method which performs data transmission withdigital multi-carrier modulation and demodulation processes utilizing areal coefficient wavelet filter bank, the communication apparatuscomprising a transmitter that performs a digital multi-carriermodulation process and a receiver that performs a digital multi-carrierdemodulation process, wherein the transmitter has: a synchronizationdata generator for generating data for synchronization that are known inthe receiver; and an inverse wavelet transformer for performing aninverse wavelet transform of the synchronization data, and the receiverhas: a wave detecting section having a first wavelet transformerinvolving M real coefficient wavelet filters, which are orthogonal withrespect to each other, for performing a wavelet transform of waveformdata of received signal; a Hilbert transformer for performing a Hilberttransform of the waveform data; a second wavelet transformer forperforming a wavelet transform of outputs from the Hilbert transformer;and a complex data generator for generating complex data, by definingoutputs from the first wavelet transformer as in-phase components ofcomplex information and outputs from the second wavelet transformer asorthogonal components of the complex information; an equalizer forperforming equalization using both complex information obtained from thewave detecting section and known signal for equalization that ispreviously assigned for the equalization process; a decision unit formaking a decision using a signal obtained from the equalizer; and asynchronization timing estimating circuit for estimating a timing ofsynchronization of symbols from phase differences between adjacentcomplex subcarriers output from the wave detecting section.
 9. Thecommunication apparatus according to claim 8, wherein the receiver has:an equalizer for obtaining an equivalent coefficient to be used for eachsubcarrier by synthesizing (2n−1)-th outputs and 2n-th outputs(1≦n≦(M/2−1), the subcarriers being numbered from 0 to M−1) with complexinformation obtained from the wave detecting section; and a decisionunit for making a decision using signal obtained from the equalizer. 10.A communication apparatus employing a multi-carrier transmission methodwhich performs data transmission with digital multi-carrier modulationand demodulation processes utilizing a real coefficient wavelet filterbank, the communication apparatus comprising a transmitter that performsa digital multi-carrier modulation process and a receiver that performsa digital multi-carrier demodulation process, wherein the transmitterhas: a synchronization data generator for generating data forsynchronization that are known in the receiver; and an inverse wavelettransformer for performing an inverse wavelet transform of thesynchronization data, and a wave detecting section of the receiver has:a wavelet transformer involving M real coefficient wavelet filters,which are orthogonal with respect to each other, for performing awavelet transform of waveform data of received signal; a complex datagenerator for generating complex data, by defining (2n−1)th outputs(n isa positive integer) from the wavelet transformer as in-phase componentsof the complex information and 2n-th outputs (where 1≦n≦(M/2−1) andsubcarriers are numbered from 0 to M−1) from the wavelet transformer asorthogonal components of the same.
 11. A communication apparatusemploying a multi-carrier transmission method which performs datatransmission with digital multi-carrier modulation and demodulationprocesses utilizing a real coefficient wavelet filter bank, thecommunication apparatus comprising a transmitter that performs a digitalmulti-carrier modulation process and a receiver that performs a digitalmulti-carrier demodulation process, wherein a modulating section of thetransmitter has: a symbol mapper for converting bit data into symboldata and mapping the symbol data to M/2 (M is a plural number) complexcoordinate planes; an inverse wavelet transformer involving M realcoefficient wavelet filters, which are orthogonal with respect to eachother; and a complex data decomposer for decomposing complex data into areal part and an imaginary part such that in-phase components of thecomplex information are supplied to the inverse wavelet transformer as(2n−1)th (n is a positive integer) inputs and such that orthogonalcomponents of the complex information are supplied to the inversewavelet transformer as 2n-th (where 1≦n≦(M/2−1) and subcarriers arenumbered from 0 to M−1) inputs.
 12. A communication apparatus employinga multi-carrier transmission method which performs data transmissionwith digital multi-carrier modulation and demodulation processesutilizing a real coefficient wavelet filter bank, the communicationapparatus comprising a transmitter that performs a digital multi-carriermodulation process and a receiver that performs a digital multi-carrierdemodulation process, wherein the transmitter has: a synchronizationdata generator for generating data for synchronization that are known inthe receiver; and a modulating section for modulating with thesynchronization data, the receiver has: a wave detecting section havinga wavelet transformer involving M real coefficient wavelet filters,which are orthogonal with respect to each other, for performing awavelet transform of waveform data of received signal; a complex datagenerator for generating complex data, defining (2n−1)th outputs(n is apositive integer) from the wavelet transformer as in-phase components ofthe complex information and 2n-th outputs (where 1≦n≦(M/2−1) andsubcarriers are numbered from 0 to M−1) from the wavelet transformer asorthogonal components of the same; and a synchronization timingestimation circuit for estimating a timing of synchronization from phasedifferences between adjacent complex subcarriers.